A simple moisture diffusion model for the prediction of optimal baking schedules for plastic SMD packages

The moisture concentration at the chip surface is the important parameter for the moisture sensitivity of the P-MQFP80 product considered here. When the critical moisture concentration at the die surface is reached, delamination occurs after soldering shock, e.g at 240°C. This critical moisture concentration, which can be determined by experiments conducted at 30°C/60% relative humidity (RH) followed by soldering shock, allows to predict the product’s moisture performance at other ambient conditions. In the case studied here, prediction was done at a customer use condition of 30°C/85% RH. Furthermore, this work showed that preconditioning of plastic packages not only induces the onset of delamination at the die surface but it appears to weaken the adhesion at this interface as well. As a result, delamination failure starts to occur earlier (i.e. within shorter moisture exposure time) in the devices tested after subsequent thermal cycling stress test. A simple moisture diffusion analytical model is proposed here for predicting the optimal baking schedules for plastic SMD packages.     

Volumetric Effects in Cross-Polarized Airborne Radar Data

In recent years the detection of soil moisture using remote sensing technology has become of interest to investigators and a variety of state and federal government agencies. The parameter of interest is important in agricultural, meteorological, biological, and hydrological applications. The use of active microwave devices has shown to provide capability for remote measurement from space. Problems do exist however, in isolating moisture information from the effects of other parameters such as roughness and vegetation. Of special concern is the suppression of the roughness effects in the radar return. This paper presents an analysis of airborne cross-polarized radar measurements of agricultural scenes. The relative responses of the system to moisture and surface roughness are presented and compared to predicted responses using radar backscatter models. It is shown that the depolarized model predictions are sensitive to soil moisture, but are much less sensitive to surface roughness effects.     

塑封IC潮敏分级及相应的使用要求

参考JEDEC标准,介绍和讨论塑封IC器件的潮敏问题,如潮敏分级,相应的包装要求,SMT回流焊温度曲线等.对涉及潮敏IC器件的电子组装应用实践中的一些问题提出参考意见.     

气密性金属封装内的水汽及气氛研究

从封装管壳、贴片材料、固化烘烤处理方式等方面,研究了封装内部的水汽和气氛。结果表明,管壳清洗后烘焙的水汽含量低于清洗后不烘焙的水汽含量。粘结材料(环氧树脂、氰酸酯树脂等)吸附于器件表面,其排放对封装内的水汽有严重的影响。对于环氧树脂H35和氰酸酯树脂JM7000两种导电胶,烘焙后的效果要好于未烘焙,且随着烘焙时间的延长,水汽含量逐步降低。对外壳清洗后进行150℃/8h的烘焙,对水汽和气氛都有好处。由于储能焊对导电胶的热冲击不大,两种导电胶的水汽和气氛排放并无明显差别。     

A Distributed and Elastic Application Processing Model for Mobile Cloud Computing

The latest developments in mobile computing technology have increased the computing capabilities of smart mobile devices (SMDs). However, SMDs are still constrained by low bandwidth, processing potential, storage capacity, and battery lifetime. To overcome these problems, the rich resources and powerful computational cloud is tapped for enabling intensive applications on SMDs. In Mobile Cloud Computing (MCC), application processing services of computational clouds are leveraged for alleviating resource limitations in SMDs. The particular deficiency of distributed architecture and runtime partitioning of the elastic mobile application are the challenging aspects of current offloading models. To address these issues of traditional models for computational offloading in MCC, this paper proposes a novel distributed and elastic applications processing (DEAP) model for intensive applications in MCC. We present an analytical model to evaluate the proposed DEAP model, and test a prototype application in the real MCC environment to demonstrate the usefulness of DEAP model. Computational offloading using the DEAP model minimizes resources utilization on SMD in the distributed processing of intensive mobile applications. Evaluation indicates a reduction of 74.6% in the overhead of runtime application partitioning and a 66.6% reduction in the CPU utilization for the execution of the application on SMD.

     

A comparison of the theory of moisture diffusion in plasticencapsulated microelectronics with moisture sensor chip and weight-gainmeasurements

In this paper, the issues pertaining to moisture diffusion in PEMs are explored and discussed. The existing models of moisture diffusion in plastic molding compounds and PEMS are reviewed. Results, modeling and analysis of moisture sorption experiments performed in this study are presented. The moisture sorption experiments were conducted on a set of PEM samples with a common type of encapsulant material to 1) characterize sorption behavior; 2) compare weight gain measurement to the measurement of moisture concentration using a moisture sensor device at the die surface; 3) assess the moisture sensor measurement method. In the case of PEM samples tested in this study, simple Fickian diffusion was shown to agree closely with the experimental results. In one case, a relatively small anomaly from Fickian diffusion was observed and was attributed to swelling and relaxation phenomena at later stages of moisture sorption in the molding compound. The calibration constants determined for the sensors in this study were found to be significantly different from those collected by the manufacturer prior to the encapsulation of the devices. This problem is believed to be degradation in sensitivity of the moisture sensor due to exposure to high temperatures and storage conditions     

Amorphous semiconductors for switching, memory, and imaging applications

Performance and reliability of amorphous semiconductor devices that deal with the handling of information in the form of switching, modulation, storage, and display are discussed. Structural changes between a disordered and a more ordered state and the concomitant large change in many material properties offer the possibility of using amorphous semiconductors for high-density information storage and high-resolution display devices. The structural changes can be initiated by various forms of energy such as an electrical pulse, a short light pulse, or a brief light exposure. Many materials show good structural reversibility. The sensitivity of an amorphous photostructural film is amplified by several orders of magnitude by first forming a latent image by photonucleation and subsequent dry development by heat or radiation. Examples of optical contrast and resolution in image formation are given. The major differences between crystalline and amorphous semiconductors are briefly outlined.     

塑封集成电路分层研究

目前塑封集成电路的分层问题越来越受到半导体集成电路封装厂商以及整机厂商的关注和重视。文章对塑封集成电路的分层产生的机理和塑封表面贴装集成电路潮湿敏感度等级的认定作了介绍。另外,对几种主要的分层失效的标准作了详细解释和说明。文章对影响塑封表面贴装集成电路分层的主要因素进行了详细的分析和说明,并对三种不同封装形式塑封集成电路的吸湿和去湿过程进行了分析和研究,并给出了结论。最后文章就如何防止分层问题提出了相应的措施。     

Near‐Stoichiometric Bulk Graphane from Halogenated Graphenes (X = Cl/Br/I) by the Birch Reduction for High Density Energy Storage

Hydrogen is a clean fuel with high specific energy and its handling and storage are important toward fuel cell research. Particularly, high‐density hydrogen storage is crucial for the viability of future hydrogen‐powered devices. This leads to the search for suitable methods; one such option is chemical storage in light materials with large surface areas, such as graphene. Here, the bulk production of graphane by Birch reduction of halogenated (Cl/Br/I) graphene precursors is reported as a potentially scalable procedure. Prior treatment with strong hydrohalic acids is used to remove oxygen‐groups and to substitute these with halogens, resulting in effective hydrogenation. An unprecedented level of hydrogen storage is obtained from the iodinated‐graphene starting material at 7.44 wt%, far above the U.S. Department of Energy's 2020 system target of 5.5 wt% and close to its ultimate 7.5 wt% goal. As the stored hydrogen is chemisorbed on the graphane scaffold it is stable at both room temperature and on atmospheric exposure, where neither temperature control nor pressure regulation is required. Hydrogen may then be desorbed at elevated temperatures above 400 °C.     

Wafer-Level Integration Technique of Surface Mount Devices on a Si-Wafer With Vibration Energy and Gravity Force

This paper reports about a novel wafer-level integration technique of discrete surface mount devices (SMDs). It enables wafer-level mounting of plural kinds of SMDs on a silicon (Si)-wafer using vibration and gravity force. Deep holes with 400-m depth are formed on the surface of a Si-wafer by deep reactive ion etching process after general integrated circuit process for positioning of SMDs. A non-conductive adhesive (CYTOP) are coated on the deep holes and it is used to fix the aligned SMDs. SMDs are distributed on a Si-wafer mounted on vibration generator, and then a vibration is applied. The SMDs migrate due to the reduced friction between the wafer surface, and they drop into the holes on the silicon wafer. The size of the holes has an appropriate clearance to the size of SMD. In order to align two or more kinds of SMDs, sizes of the deep holes on a Si-wafer are adjusted to the size of each SMD. SMDs with the largest size are dropped into the holes first, and then the secondary large SMDs are dropped into the holes with the corresponding size. SMDs are finally connected electrically by wire bonding at the final step. In the experiment, two different sizes of SMD were successfully mounted into all the holes on a Si-wafer automatically. This technology will be a wafer-level process technology which is very promising to integrate two or more kinds of discrete elements.     

Modeling moisture ingress through polyisobutylene‐based edge‐seals

Photovoltaic devices are often sensitive to moisture and must be packaged in such a way as to limit moisture ingress for 25 years or more. Typically, this is accomplished through the use of impermeable front and backsheets (e.g., glass sheets or metal foils). However, this will still allow moisture ingress between the sheets from the edges. Attempts to hermetically seal with a glass frit or similarly welded bonds at the edge have had problems with costs and mechanical strength. Because of this, low diffusivity polyisobutylene materials filled with desiccant are typically used. Although it is well known that these materials will substantially delay moisture ingress, correlating that to outdoor exposure has been difficult. Here, we use moisture ingress measurements at different temperatures and relative humidities to find fit parameters for a moisture ingress model for an edge‐seal material. Then, using meteorological data, a finite element model is used to predict the moisture ingress profiles for hypothetical modules deployed in different climates and mounting conditions, assuming no change in properties of the edge‐seal as a function of aging. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural Transformation of Acrylic Resin upon Controlled Electron‐Beam Exposure Yields Positive and Negative Resists

Zwitter polymers are defined as polymers that undergo transformation from a linear to a crosslinked structure under electron‐beam irradiation. A resist polymer may be either linear or crosslinked, depending on electron‐beam dosage. The structural transformation of acrylic resin make it suitable for applications in positive and negative resists in the semiconductor field. The contrast ratio and threshold dose both increase with increasing resist thickness for both the positive and negative resists, while the positive resist exhibits better contrast than the negative. The intensity of the characteristic Fourier‐transform infrared absorption band at 1612 cm^–1 (vinyl group) is used to explain the phenomena behind these resist transformations. We evaluate the effects of two important processing conditions: the soft baking and post‐exposure baking temperatures. Pattern resolution decreases upon increasing the baking temperature, except for soft baking of the negative resist. The effect of electron dose on the pattern resolution is also discussed in detail for both resists. High electron‐beam exposure does not improve the etching resistance of the resist because of the porous nature of the resist that develops after high‐dosage irradiation.     

Ambient Processable and Stable All‐Polymer Organic Solar Cells

In this work, the way in which ambient moisture impacts the photovoltaic performance of conventional PCBM and emerging polymer acceptor–based organic solar cells is examined. The device performance of two representative p‐type polymers, PBDB‐T and PTzBI, blended with either PCBM or polymeric acceptor N2200, is systemically investigated. In both cases, all‐polymer photovoltaic devices processed from high‐humidity ambient conditions exhibit significantly enhanced moisture‐tolerance compared to their polymer–PCBM counterparts. The impact of moisture on the blend film morphology and electronic properties of the electron acceptor (N2200 vs PCBM), which results in different recombination kinetics and electron transporting properties, are further compared. The impact of more comprehensive ambient conditions (moisture, oxygen, and thermal stress) on the long‐term stability of the unencapsulated devices is also investigated. All‐polymer solar cells show stable performance for long periods of storage time under ambient conditions. The authors believe that these findings demonstrate that all‐polymer solar cells can achieve high device performance with ambient processing and show excellent long‐term stability against oxygen and moisture, which situate them in an advantageous position for practical large‐scale production of organic solar cells.     

A Technique for Optimal Sequential Maintenance Scheduling

This paper presents the mathematical development of, and a simple solution technique for, an optimal sequential maintenance scheduling problem. The model is shown to satisfy the Kuhn-Tucker conditions, the necessary and sufficient conditions for the existence of an optimal solution. Real-world systems consisting of mixtures of constant and increasing failure rate devices are considered in the model. Sequential preventive maintenance schedules are developed for groups of identical items with increasing failure rates. Provision is made for the corrective maintenance of these groups if failures occur in between the preventive maintenance schedules. Also, constant failure rate devices are accorded corrective maintenance when failures occur. Optimality is achieved by minimizing the total annual maintenance cost, subject to constraints on the system availability, number of maintenance personnel and intervals of preventive maintenance. The model is applied to a coal mine power system example.     

Compensation-circuit to improve radiation-hardness in GaAsdigital-circuits, based on X-ray studies

Earlier results have shown that GaAs devices do not exhibit appreciable degradation up to a radiation dose of nearly 10⁸ rad (GaAs). The results of this work suggest that GaAs devices and circuits are sensitive to radiation exposure at dose levels below 10⁸ rad(GaAs). Degradation was observed in E-MESFET and D-MESFET parameters and in circuit performance for devices which were designed and fabricated in a 1.2 μm GaAs process, when exposed to varying doses of 1.49 keV X-rays in the range 40-65 Mrad (GaAs). The degradation is attributed to the change in the properties of the MESFET channel region, caused by the transport of the atomic hydrogen from the passivation layer to the channel. A compensation circuit, based on the observed behavior of radiation effects on GaAs devices, has been designed to improve the radiation insensitivity of GaAs (E/D) based circuits under SPICE (Simulation Program with IC Emphasis) simulated conditions. Its usefulness is demonstrated through a DCFL inverter circuit up to nearly 10⁸ rad (GaAs) dose level. The results of this work can be used in the design of complex-function radiation-insensitive DCFL based circuits     

FCBGA器件PCB组装应用的若干要点

介绍FCBGA器件PCB组装应用时需要考虑的若干要点.内容包括器件的潮敏控制及干燥包装袋暴露后器件潮敏寿命的再定级,提供了器件的再烘烤参考条件.也涉及相应SMT组装工艺的一些注意要点以及PCB返修时的注意要点,提供FCBGA器件在PCB组装返修时回流焊温度曲线的参考指南.     

Resource allocation strategies for survivability in WDM optical networks

WDM optical networks are high speed networks and provide enormous capacity. Survivability is very important issue in these networks. Survivability requires resources for handling the failures. So, efficient resource allocation strategy is required for survivability. In this paper, we have presented two resource allocation strategies for survivability. These strategies reserve the resources for the primary lightpaths and backup lightpaths. Then extensive simulations are done on different networks to evaluate the performance in terms of blocking probability. The results show that the second strategy performs better than first strategy.     

Demonstrated reliability of plastic-encapsulated microcircuits formissile applications

For the past decade, overall reliability improvement and product availability have enabled plastic encapsulated microcircuits (PEM) to move from consumer electronics beyond the relatively large and reliability-conscious automotive market, into the military market. Based on the analysis of the worst-case PEM scenario for military applications, demonstrating the moisture reliability under long-term (20 years) dormant storage environments has become the last hurdle for PEM. Studies have demonstrated that PEM can meet the typical missile environments in long-term storage. To further validate PEM reliability in missile applications, Texas Instruments (TI) conducted three separate studies involving 6 years of PEM moisture-life monitoring and assessment, testing of the standard PEM electrical characteristics under the military temperature ranges (-55°C to +125°C), and assessing their robustness in moisture environments after the assembly processes. These TI studies support the use of PEM in missile (or similar) applications. Effective focus on part and supplier selection, supplier teaming, and process monitoring is necessary to maintain the PEM reliability over the required environments at the lowest cost. This paper assesses PEM reliability for a selected missile storage environment using the industry-standard moisture testing, such as biased HAST or 85°C/85%RH (relative humidity), for demonstrating the PEM moisture survivability. The moisture reliability (MTTF) or average moisture lifetime of PEM is assessed to correlate PEM capability to anticipated field-performance environments